(a) Technical Field
The present invention relates to a pressure control actuator (PCA) assembly of a hydrogen supply system in a fuel cell vehicle. More particularly, the present invention relates to an integrated pressure control actuator assembly of a hydrogen supply system in a fuel cell vehicle, which allows the fuel cell vehicle to be driven in a limp home mode in the event of an emergency by adjustment of the pressure of hydrogen.
(b) Background Art
A fuel cell vehicle is driven by electrical energy generated by an electrochemical reaction between hydrogen as a fuel and oxygen in the air in a fuel cell stack of the vehicle. Since the fuel hydrogen has a large volume in a gaseous state, methods of storing hydrogen in the form of a high-pressure gas, a liquid hydrogen, or a metal hydride have been studied. According to a method of storing high-pressure hydrogen gas in a high-pressure hydrogen tank at 350 bar or 700 bar, since the high-pressure hydrogen gas cannot be directly supplied to the fuel cell stack, the pressure of hydrogen gas is reduced so as to supply hydrogen gas at low pressure (generally, below 1 bar) to the fuel cell stack.
FIG. 1 shows a conventional hydrogen supply system of a fuel cell vehicle, which reduces the pressure of high-pressure hydrogen gas and supplies hydrogen gas under reduced pressure to a fuel cell stack. In the hydrogen supply system, the pressure of hydrogen is reduced in two steps.
More specifically, as shown in FIG. 1, hydrogen gas at high pressure (350 or 700 bar) supplied from a fuel storage tank transported to a high-pressure regulator. The high-pressure regulator reduces the pressure of hydrogen to 5 to 20 bar. The reduced pressure hydrogen is then sent to a low-pressure regulator connected to a start/stop solenoid valve for supplying hydrogen gas or cutting off the supply (refer to reference numeral 10 in the figure). The low-pressure regulator reduces the pressure of the hydrogen to a pressure that allows supply of the hydrogen gas to the fuel cell stack (e.g., 1 bar or lower).
The hydrogen gas transported from the low-pressure regulator is supplied to the fuel cell stack through an ejector and reacts with oxygen in the air supplied to the fuel cell stack, thus generating electrical energy.
In this case, the hydrogen gas that does not participate in the reaction with oxygen is recirculated to the fuel cell stack through a recirculation blower and the hydrogen gas that is not recirculated is discharged to the outside through a purge solenoid valve of a hydrogen discharge system.
The conventional hydrogen supply system, however, has drawbacks. More particularly, the low-pressure regulator of the system controls the pressure of hydrogen by movement of upper and lower springs while atmospheric pressure is maintained in a reference pressure space. It thus supplies hydrogen gas passively and cannot actively increase the supply amount of hydrogen. To increase the supply amount, a separate hydrogen recirculation system is required. Moreover, when water is accumulated in a fuel electrode (anode), it cannot discharge the water by forcibly increasing the supply amount of hydrogen gas or the pressure of hydrogen gas.
FIG. 2 is a graph showing a change in hydrogen supply pressure according to an output of the conventional hydrogen supply system including the low-pressure regulator. It can be seen from FIG. 2 that the pressure of a fuel electrode (anode) showing the supply pressure of hydrogen passing through the low-pressure regulator is reduced as the output of the fuel cell stack is increased. Accordingly, in the low-pressure regulator, the higher the output of the fuel cell stack, i.e., the higher the flow amount of hydrogen gas, the lower the hydrogen supply pressure. With the decrease in the hydrogen supply pressure, the pressure unbalance between the fuel electrode and an air electrode (cathode) is caused, thereby increasing the amount of hydrogen crossover during idle and decreasing the performance of the fuel cell stack in the event of high load.
Moreover, as shown in FIG. 3, in the conventional hydrogen supply system including the low-pressure regulator, since a start/stop solenoid valve 20 and the lower pressure regulator 30 are connected to each other through a pipe 40, a number of leakage points (not shown) occur in the system, resulting in leakage of hydrogen.
In another conventional hydrogen supply system, a pressure control actuator is used instead of the low-pressure regulator. While the low-pressure regulator, as discussed above, supplies hydrogen gas passively and cannot actively increase the supply amount of hydrogen, the pressure control actuator can actively control flow and pressure as well.
The system including the pressure control actuator, however, has problems in that, in the event that a failure occurs in the pressure control actuator, the supply of hydrogen gas is cut off to stop the vehicle operation, which may result in a serious accident and that in the event that the fuel cell system is shut down due to the fuel cut, none of alternative way to make the vehicle continue to be operated is not provided.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.